The problem of insulation is a concern of increasing importance throughout the world in view of the current energy crisis. Of particular interest is the problem of providing thermal insulation which does not interfere with the passage of radiation, such as light and heat in one direction.
One practical example of a system which requires insulation for enhanced efficiency is the solar pond which is described in the following reference: H. Weinberger, The Physics of the Solar Pond, Solar Energy, Volume 8, page 45 (1964). In order to lower the significant heat losses to the atmosphere at the surface of the pond, it is considered desirable to provide some sort of stable air layer between the pond surface and the atmosphere. The construction of such an air gap over a relatively large area does not appear to be feasible due to the difficulty of providing and maintaining in place over the pond a cover which is transmissive to solar radiation. U.S. Pat. No. 4,091,800 describes a solar pond construction which inter alia may comprise a foam formed of a sudsing agent as in fire-fighting foams disposed on the top surface thereof. No technique for retaining the foam in place is disclosed or suggested.
Various types of apparatus for assisting solar heating of swimming pools are disclosed in the following U.S. Pat. Nos.: 4,016,015; 4,121,567; 4,137,612; 4,106,905; 3,072,920; 4,195,622; 3,949,095; 4,222,366 and 4,256,087. None of these disclose a multilayered construction for enhancing solar radiation transmissivity, while limiting thermal infra-red back radiation.